The present invention relates to a system for ensuring regular information "refreshing" of the storage elements of a semiconductor read-write memory in electronic binary data processing apparatus.
In recent times, semiconductor storage systems have been largely employed as the main memories in data processing apparatus. These memories, which are produced as large-scale integrated circuits having high density and a high number of elements, have shown remarkable advantages over conventional memories employing magnetic elements, with regard to operating speed, fabrication costs, and reliability. However, their use requires peculiar care, in view of the fact that they are intrinsically "volatile", that is, the registered information fades out with the passing of time and may become completely lost. Therefore, these memories must be "refreshed" periodically; that is, the stored information must be rewritten; and it is necessary to make sure that this refreshing operation is carried out within a defined time interval from the previous such operation.
Prior information refreshing systems refresh the whole memory, row after row in succession, at the end of the maximum time interval allowed. This method has the drawbacks of submitting the whole system to a massive power demand in a single small time interval and of requiring the stopping of all normal memory operation during this interval; it is also subject to the risk that in case the refreshing is not carried out, for any accidental reason, the memory content may be partially or totally lost.